In the case of usual tools of the generic type (see, for example German patent specification 3710929 and its equivalent U.S. Pat. No. 4,831,711) used for clinch joining, the punch has a pin with a smaller diameter, by means of which the plates to be joined are deep drawn and squashed in a blind hole to achieve a firm joint between the plates. Other generic methods are also known, whereby tools, comprising a punch and die, are used for pressing, stamping or the like of plates, also, inter alia, for joining parts on the plates (German published patent application 19913695).
In the case of a joining it is also known to strongly cool the tools on the side of the punch and/or of the die, i.e. the punch and the die, thus enabling the joining of plates partly made from polymers or contain polymers with one another (German published patent application 19752201). By virtue of this it will be achieved that when plates made of visco-elastic materials, like polymers, rubber, etc. are processed with other materials, like for example metal, similar physical prerequisites will be present making such a joining possible. Such composite tools are, of course, expensive and are used only when the application or the necessity is appropriate.
In the case of another known method of the generic type (German published patent application 10006789) special attention is given regarding the mounting of the tool, i.e. of the punch or the die, in the tool holder of the machine, the aim being a favourable exchange of these tools, for the purpose of which an appropriate radial displaceability is provided.
Basically, but also in all of these cases, the sections of the tool directly affected by the work process, are particularly stressed, The tool life of the tools used on this occasion corresponds to the use and requirements of the material of the tool and in many cases is unsatisfactorily short. To achieve the accepted standard, the expense connected with the manufacture of the tools is very high, since they have to have an appropriate hardness in the stressed region. On the other hand such hardness may lead to a breakage of the tool, especially when an often required considerable longitudinal extension at right angle to the working direction is present. In addition, due to the mounting a minimum longitudinal extension in the working direction is necessary; this means that due to these conditions the punch and the die, having a hardness necessary for a long tool life, have a certain tendency to break, while such a breakage can have disastrous consequences. Particularly when the tool is used in the serial production for the joining of sheet metals for motor vehicles has such a shortcoming disastrous consequences. Thus the aim is always a tool with an optimum tool life with extremely favourable hardness and only slight tendency to break.